Originally Posted by KarenPDX
Has anybody done this with a suitcase solar panel? On my 21C there's a Victron DC/DC charger in-between the 7 pin plug and the battery busses.
Is my thinking right that the Victron unit could function as a charge controller for the battery or should I use the onboard charge controller as well?
We are headed to AZ in a couple of days and I'm hoping to do some experiments to find the best way to use a suitcase solar panel on my rig.
The Renology unit is easily configured to use the onboard controller or by pass it so I though I would do the following and look at the current flowing across my shunt.
1) Solar suit case wired in parallel with the roof top panels and the solar side of the GoPower charge controller. (The factory wired auxiliary solar port)
2) Hook up the solar suitcase to the battery side via a seven pin pigtail connector to the the trailer wiring. Use of onboard charge controller on the suitcase pending input from the community.
3) Direct connection to battery bank of solar suitcase. Suitcase charger controller in use.
4) As above, but wire battery bank with standalone charger controller and then hook the suitcase to the standalone charge controller.
I see a potential issue with using the Victron DC/DC converter with a solar panel. The reason the DC/DC converter is in the circuit in the first place is to boost
the voltage from the tow vehicle to a voltage suitable to charge Lithium batteries (around 14.4 to 14.8). Tow vehicles - mine included - are not designed to get the correct voltage from the alternator all the way back to the trailer batteries. The DC/DC boost function expects a lower voltage coming in as opposed to the voltage going out (12 V in and 14.6 V out, for example). Whereas the panel - with its internal controller bypassed - should be providing typically 18 V or more if unloaded. I don't know about the Victron specifically, but I do know that some DC/DC converters will pass the higher voltage without any regulating - potentially applying 18 V to the batteries and anything running.
I personally use the #1 solution - for the last 8 years. Parallel the unregulated remote panel voltage to the GoPower regulator. It is quite happy with the extra power and I watch the current about double going into the batteries.